This invention relates to rubber modified styrene polymers having as the result of incorporation therein of new tin sulfide compounds improved color, processability, and mechanical properties and retention of these properties upon exposure to elevated temperatures.
Rubber modified styrene polymers are well known. Since the pioneer disclosure of I. Ostromislensky in U.S. Pat. No. 1,613,673 of Jan. 11, 1927, an increasing number of rubber modified styrene polymers has become available in growing quantities. In a 1970 published review of styrene polymers, R. Boyer has quoted estimates that of a total 1969 U.S. production of 1,400,000 tons of styrene polymers (excluding styrenebutadiene synthetic rubber), 57% represent such rubber modified styrene polymers as "high impact" butadiene modified styrene polymer and acrylonitrile-butadiene-styrene (ABS polymers); see N. Bikales (editor), Encyclopedia of Polymer Science and Technology (J. Wiley-Interscience, New York), volume 13, Pages 443 to 446.
The various kinds of rubber modified styrene polymers have in common a two phase or "domain" structure in which hard, glassy portions and softer, elastomeric portions can be distinguished. The rubber modified styrene polymers also share excellent impact properties and can even impart these properties to blends with other hard, glassy polymers, for example the well known impact resistant blends of polyvinyl chloride (PVC) with ABS polymer.
Unmodified ("general purpose" or "crystal") polystyrene is thermally very stable, and is routinely processed at 200.degree.-250.degree. C without objectionable degradation being noticed. The excellent heat stability of unmodified polystyrene is such that molten polymer from each of several polymerization reactors can be fed to a holding tank and from there to extruders as required, thus being kept molten for considerable periods (see Boyer, ibid. pages 131-133) above 200.degree. C.
Rubber modified styrene polymers, on the other hand, are subject to oxidative and thermal degradation at temperatures of 150.degree. C and higher, and stabilization is required to make satisfactory processing possible with minimal changes in melt viscosity, impact strength, and color.
W. Cummings in U.S. Pat. No. 3,267,069 of Aug. 16, 1966 disclosed stabilization against discoloration and degradation of physical properties of ABS polymer by a mixture of zinc sulfide and an ester of 3,3'-thiodipropionic acid such as dilauryl, distearyl, and ditridecyl thiodipropionate. The ABS polymers generally contain 15 to 35 weight % acrylonitrile, 5 to 35% butadiene, and 40 to 80% styrene based on the entire ABS polymer as 100%. The ABS polymer can be a graft copolymer prepared by polymerizing acrylonitrile monomer and styrene monomer in a previously prepared polybutadiene latex or butadiene copolymer rubber latex, or a physical blend of separately prepared acrylonitrile-styrene resin and butadiene-acrylonitrile rubber. C. Bawn, in U.S. Pat. No. 3,352,820 of Nov. 14, 1967 disclosed an ABS plastic composition containing a conventional antioxidant or mixture of antioxidants such as alkylphenyl phosphite and methylenebisalkylphenol, with a Group II metal sulfide added for stabilization against discoloration at elevated temperatures. C. Tholstrup in Canadian Pat. No. 750,469 of Jan. 10, 1967 disclosed the stabilization of an ABS resin, a polyacrylonitrile, a polybutadiene, a polyisoprene, a polychloroprene, and a copoly(butadiene-styrene) resin with a stabilizer mixture consisting essentially of a dialkyl thiodialkanoate and an alkylenebisphenol with the addition of organic phosphite optional. Sanyo Chemical in Japanese Patent publication 14324/68 of June 17, 1968 disclosed improving thermal resistance of ABS resin with a lithium, sodium, potassium, calcium, or magnesium salt of a phosphoric acid ester of an organic hydroxy compound having a hydrocarbon group of at least 6 carbon atoms. K. Ott in U.S. Pat. No. 3,414,636 of Dec. 3, 1968 disclosed copolymer mixtures of a butadiene elastomer and a thermoplastic copolymer of styrene and acrylonitrile having excellent thermal stability as a result of admixing a small amount of composition consisting of 2,2'-methylenebis-4-methyl-6-cyclohexylphenol and zinc sulfide. Ott's copolymer mixtures are defined as 5 to 60% by weight of rubber-elastic copolymer of butadiene and 95 to 40% by weight of thermoplastic component consisting of 50 to 95% styrene and 50 to 5% acrylonitrile. A. Hecker in U.S. Pat. No. 3,472,813 of Oct. 14, 1969 disclosed a stabilizer composition for ABS polymers consisting essentially of an alkyl pyrophosphate salt of a monovalent or bivalent metal cation or an ammonium, quaternary ammonium, or amine cation, and a polyhydric polycyclic phenol, and in U.S. Pat. No. 3,520,952 of July 21, 1970 the same stabilizer composition for block copolymers containing a non-elastomeric block which is a polymer of an alpha-olefin, and an elastomeric block which is a polymer of a conjugated diolefin. P. Marinacci in U.S. Pat. No. 3,637,555 of Jan. 25, 1972 disclosed a multi-component combination of antioxidants for stabilizing ABS type copolymers subject to oxidative and heat degradation, containing a diester of thiodipropionic acid, 2,6-di-t-butyl-4-methylphenol, a 2,2'-methylenebis(4-alkyl-6-t-alkylphenol), and an epoxide compound, with the optional use in addition of an alkylated aromatic phosphite and calcium stearate. C. Abramoff in U.S. Pat. No. 3,856,728 of Dec. 24, 1974 disclosed a stabilizer system for ABS polymers, both pigmented and unpigmented, comprising an organic phosphite, a polyhydric polycyclic phenol, and an epoxy compound. T. Ohzeki in Japan Kokai No. 4244/76 of Jan. 14, 1976 disclosed ABS resin and high-impact butadiene-modified polystyrene comprising an organic phosphite and a pinene-substituted bisphenol. A. Kennedy in U.S. Pat. No. 3,907,932 of Sept. 23, 1975 disclosed the stabilization of olefinic nitrile polymers including copolymers with styrene and butadiene containing at least 50% of the olefinic nitrile with dialkyltin maleate compounds having the formula (R.sub.2 SnC.sub.4 H.sub.2 O.sub.4).sub.x or R.sub.2 Sn(C.sub.4 H.sub.2 O.sub.4 R').sub.2 in which R is alkyl with 2 to 12 carbons, R' is alkyl with 4 to 14 carbons and x is an integer from 1 to 4.
Kennedy points out that a number of other alkyltin compounds known as stabilizers for polyvinyl chloride (PVC) are unsatisfactory in her polymers. Earlier disclosures of tin compounds in rubber modified styrene polymers include ABS polymer with 0.02-10% of (R.sub.1 R.sub.2 R.sub.3 Sn).sub.a X where R.sub.1 and R.sub.2 are hydrocarbon, R.sub.3 is hydrocarbon or X, X, is thiol acid, aliphatic or aromatic mercaptan, or an ester thereof, by Nitto Kasei Co. in Japanese publication No. 16187/66 of Sept. 12, 1966; also dialkyltin aliphatic carboxylates together with phosphite diesters and triesters by M. Watanabe in Japan publication 22531/67 of Nov. 4, 1967.
There is an enormous number of disclosures of tin compounds used to stabilize PVC compositions, some of which contain minor amounts of ABS polymers to improve impact resistance. To illustrate the unmanageably large bulk of this literature, it might be noted that a 1959 review booklet by H. Verity Smith titled "The Development of the Organotin Stabilizer" (published by Tin Research Institute, Greenford, England) listed over 100 patent disclosures of tin containing stabilizers for PVC, and more recently C. Stapfer in U.S. Pat. No. 3,830,751 of Aug. 20, 1974 listed over 500 individual tin containing compounds and L. Weisfeld in U.S. Pat. No. 3,887,519 of June 3, 1975 listed over 200 compounds that are all methyltin derivatives, i.e. compounds with at least one methyl group directly linked to tin, including for example dimethyltin sulfide. Overwhelmingly the tin containing stabilizers referred to in this literature are tin compounds having at least one hydrocarbon group linked to 4-valent tin through carbon, for example methyl, n-butyl, and n-octyl. The remarkably small number of disclosures of tin containing stabilizers other than 4-valent tin derivatives with at least one hydrocarbon group linked to tin are represented by J. Fincke U.S. Pat. No. 2,479,918 of Aug. 23, 1949, tetra(2-thienyltin); S. Caldwell U.S. Pat. No. 2,629,700 of Feb. 24, 1953, carboxylate salts of 2-valent (stannous) tin; W. Leistner U.S. Pat. No. 2,726,227 of Dec. 6, 1955, certain tetrahydrocarbon mercaptides of tin having only hydrocarbon groups linked to tin through sulfur; W. Considine in U.S. Pat. No. 3,412,120 of Nov. 19, 1968 disclosed cyanoalkylenetin sulfides having linked to tin one or two cyanoalkylene groups having two or more carbon atoms in the alkylene group made from tetrakis (cyanoalkylene)tin by halogenation or redistribution to the required cyanoalkylenetin halide; Considine also showed in U.S. Pat. No. 3,454,609 of July 8, 1969 that when cyanoalkylenetin compounds were hydrolyzed, polymeric propionatotin compounds were obtained. Akzo N.V. in Netherlands Specification 74-12230 of Mar. 16, 1976 disclosed functional substituted organotin trihalides prepared from stannous halide, hydrogen halide, and carbonyl group activated olefins of the type R.sub.1 R.sub.2 C.dbd.CR.sub.3 R.sub.4 where at least one R group is an activating group with a carbonyl radical adjoining the double bond and the other R groups are hydrogen or alkyl groups, and converted to mercaptoester type stabilizers; Akzo N.V. Netherlands Specification No. 75-03116 of Sept. 17, 1976 disclosed functional substituted organotin dihalides prepared from tin metal, hydrogen halide, and carbonyl group activated olefins of the type R.sub.1 R.sub.2 C.dbd.CR.sub.3 R.sub.4 where at least one R group is an oxygen containing group with a carbonyl group adjoining the double bond and the other R groups are hydrogen or alkyl groups, and converted to stabilizers by reaction with alkylthiocarboxylic acid esters, alkylthiols, monocarboxylic acids, or partial esters of dicarboxylic acids.
Pertinent to the evaluation of the present invention among the large number of known hydrocarbontin sulfur compounds are particularly the use of hydrocarbontin sulfides by E. Weinberg in U.S. Pat. Nos. 2,746,946 of May 22, 1956 and 2,789,103 of Apr. 16, 1957; and by M. Crauland in U.S. Pat. No. 3,108,126 of Oct. 22, 1963; alkylstannonic acids and alkylthiostannonic acids (i.e. monohydrocarbontin sulfides) by H. Frey in U.S. Pat. No. 3,021,302 of Feb. 13, 1962; cyclic dihydrocarbyltin salts of mercapto carboxylic acids by G. Mack in U.S. Pat. No. 3,027,350 of Mar. 27, 1962; thiobis (dihydrocarbontin) salts of carboxylic acids and dicarboxylic acid monoesters by A. Schroeder in U.S. Pat. No. 3,476,404 of Nov. 4, 1969; an organotin stabilizing agent obtained by reacting a compound of the formula R--Sn--(X).sub.3 wherein R is a hydrocarbon and X halogen, with a mixture of an alkali metal sufide and (a) aliphatic alkali metal mercaptide or (b) an alkali metal salt of a saturated or unsaturated mono or polycarboxylic acid, by C. Dorfelt in U.S. Pat. No. 3,442,852 of May 6, 1969; organotin mercaptoacid ester sulfides having the formula: ##STR1## in which n is an integer from one to two, m is the number of COOR.sub.1 groups, and is an integer from one to four, x is an integer from zero to one, R is a hydrocarbon radical having from about one to about eighteen carbon atoms, and preferably from four to eight carbon atoms, R.sub.1 is an organic group derived from a monohydric or polyhydric alcohol of the formula R (OH).sub.n4, where n.sub.4 is an integer from one to about four, but is preferably one or two; R.sub.2 is R or SZ (COOR.sub.1).sub.m ; Z is a bivalent alkylene radical carrying the S group in a position alpha or beta to a COOR.sub.1 group, and can contain additional free carboxylic acid, carboxylic ester, or carboxylic acid salt groups, and mercapto groups; and the Z radical has from one to about five carbon atoms, by O. Kauder in U.S. Pat. No. 3,565,930 of Feb. 23, 1971; reaction products of organotin mercaptoacid derivatives having the formula ##STR2## as well as R.sub.n S.sub.n (SR'COOR").sub.4-n and (RSn(SR'COOR").sub.2).sub.2 X wherein R is an alkyl radical having up to 12 carbons, R" is an alkyl radical, R' is an alkylene group of at least 2 methylene groups, X is oxygen or sulfur, n is 1 to 3 and y designates the degree of polymerization, with an organotin oxide, a monohydrocarbyltin oxide, or a hydrocarbylstannoic acid or ester thereof, by L. Weisfeld in U.S. Pat. No. 3,576,785 of Apr. 27, 1971; and alkyltin polysulfide thioesters having the formula (R.sub.x Sn).sub.n (--SR'COOR").sub.(4-x)n-2m (--S.sub.y).sub.m where the tin is tetravalent, R is alkyl of 1 to 8 carbon atoms or benzyl, R' is alkylene of 1 to 4 carbon atoms, R" is alkyl of 1 to 18 carbon atoms or alkenyl of 2 to 18 carbon atoms, cycloalkyl having 5 to 6 carbon atoms in the ring, or benzyl, x is 1 or 2, y is 2 to 4, n is 1 to 10 and m is 1/2n to n, by T. Kugele in U.S. Pat. No. 3,869,487 of Mar. 4, 1975.